Simulations of Hydrological Cycle Changes Between the LGM and the Present Day over China

Based on the International Satellite Cloud Climatology Project (ISCCP) data in 1983-2006, it is found that there is a high value center of high cloud amount over the Tibetan Plateau (TP), while there is a high value center of middle cloud amount over the Sichuan Basin extending to the coastal area of southeastern China along the same latitude, and a low one over the TP. The present day (PD) and Last Glacial Maximum (LGM) climates are simulated by using the NCAR Community Climate Model (CCM3) nested with a regional mesoscale model (MM5). Comparing the clouds simulated by MM5 with the ISCCP data, it is found that the main patterns of high and middle clouds over China can be reproduced by MM5, which implies that the climate characteristics of clouds might be dominated by relative humidity. Meanwhile, the vertical distributions of water vapor and temperature are also well simulated by MM5. Furthermore, the hydrological cycle changes between the LGM and PD simulations are examined. The results show that during the LGM,the tropospheric temperature decreases in summer with a high value reduction center in the upper and middle troposphere; in winter, a high value reduction center of temperature appears in the middle troposphere over southern China, while the temperature in the upper and middle troposphere increases over northern China. There obviously exists a positive correlation between the water vapor content and temperature change. The water vapor content mostly decreases with the maximum drop in the near-ground surface layer, but it increases in the upper and middle troposphere over northern China in winter.Changes of water vapor content gradually weaken with the altitude increasing, reaching the minimum in the upper troposphere. The relative humidity can either increase or decrease with the maximum change greater than 15%. It is not conservative on the regional scale, and its change is consistent with the changes of middle and low clouds. During the LGM, the high cloud reduces nationwide except over Southwest China,and the middle and low clouds also decrease with the greatest reduction seen in the low cloud. Precipitation changes correspond to the changes of middle and low clouds. Based on the changes of the relative humidity and effective precipitation, it is found that during the LGM, Southwest China is wetter in summer, so is Northwest China.